1. Field of the Invention
This invention relates generally to a power management system in a base station transceiver system. In particular, the present invention allocates power to channels on a demand-based system for the base station transceiver system.
2. Background of the Invention
A conventional cellular phone system 1300 is shown in FIG. 1. As illustrated in FIG. 13, the cellular phone system 1300 includes a plurality of cells 1310a, 1310b, a mobile unit 1320, a plurality of base transceiver stations (BTS) 1305a, 1305b, communication lines 1340, a mobile telecommunications switching office (MTSO) 1330, an interface 1350 and a switched telephone network 1360.
The cellular phone system 1300 has a fixed number of channel sets distributed among the BTS 1305a, 1305b serving a plurality of cells 1310a, 1310b arranged in a predetermined reusable pattern. The mobile unit 1320, in a cell 1310a or 1310b, communicates with the BTS, 1305a or 1305b, respectively, via radio frequency (RF) means. The BTS 1305a, 1305b communicate with the MTSO 1330 via communication lines 1340. The MTSO 1330 communicates with the switched telephone network 1360 via the interface 1350.
In the cellular phone system 1300, the cell areas typically range from 1 to 300 square miles. The larger cells typically cover rural areas, and the smaller cells typically cover urban areas. Cell antenna sites utilizing the same channel sets are spaced by a sufficient distance to assure that co-channel interference is held to an acceptably low level.
The mobile unit 1320 in a cell 1310a has radio telephone transceiver equipment which communicates with similar equipment in BTS 1305a, 1305b as the mobile unit 1320 moves from cell to cell.
Each BTS 1305a, 1305b relays telephone signals between mobile units 1320 and a mobile telecommunications switching office (MTSO) 1330 by way of the communication lines 1340.
The communication lines 1340 between a cell site, 1310a or 1310b, and the MTSO 1330, are typically T1 lines. The T1 lines carry separate voice grade circuits for each radio channel equipped at the cell site, and data circuits for switching and other control functions.
The MTSO 1330 in FIG. 1 includes a switching network (not shown) for establishing call connections between the public switched telephone network 1360 and mobile units 1320 located in cell sites 1310a, 1310b and for switching call connections from one cell site to another. In addition, the MTSO 1330 includes a dual access feeder (not shown) for use in switching a call connection from one cell site to another. Various handoff criteria are known in the art and utilize features such as phase ranging to indicate the distance of a mobile unit from a receiving cell site, triangulation, and received signal strength to indicate the potential desirability of a handoff. Also included in the MTSO 1330 is a central processing unit (not shown) for processing data received from the cell sites and supervisory signals obtained from the switched telephone network 1360 to control the operation of setting up and taking down call connections.
In order to remain competitive in an increasingly crowded market, wireless equipment manufacturers experience constant pressure to reduce their costs. One way to reduce the overall cost of a cellular phone system is to re-design individual system components to operate at a lower cost.
In the conventional cellular phone system, the power amplifier used in a BTS is a significant factor contributor to the overall cost of the BTS. As one of the most expensive components, it would be desirable to have the power amplifier operate as efficiently as possible in terms of power usage, in order to minimize the hardware requirements for this high cost component.
In a typical broadband Base Transceiver System that supports multiple conversations with mobile stations on different frequencies, each carrier signal must be amplified separately. It is possible to provide a single power amplifier for each carrier, along with a frequency selective combiner. This architecture suffers significant loss of efficiency due to the insertion losses encountered in the frequency combiner. Perhaps more significantly, the frequency combiner is physically large, with and typically has xe2x80x9cstaticxe2x80x9d frequency selectivity which needs to be manually tuned during base station installation and reconfiguration. The efficiency of a single carrier power amplifier installation can be improved through the installation of antenna combiners, an architecture that generally requires mast mounted power amplifiers, which increases the required geographic area for the base station installation. The arrangement of small power amplifiers in an array, using spatial combination of a number of antenna elements instead of one central power amplifier per antenna, improves the physical space requirements of the system, but it still requires multiple antenna installations, and accordingly requires a relatively large physical space in which to locate the installation.
The installation of a single, high-power multi-carrier power amplifier (MCPA) will overcome these drawbacks of the single carrier power amplifier installation. However, a common limitation of the multi-carrier amplifier is linearityxe2x80x94that is, the typical MCPA provides a fixed amount of power for each carrier in the BTS in a technique known as the xe2x80x9cdivide among carriersxe2x80x9d scheme.
This fixed division of power has some drawbacks. For instance, a fixed amount of power for each carrier necessarily limits the distance that the broadband BTS can transmit. When a carrier wave is initially transmitted, the strength of the carrier wave is close to the fixed amount of power assigned to that carrier. As the carrier wave propagates through space, the power decreases, varying inversely proportionally to the transmission distance R raised to the fourth power, i.e.   Power  ∝      1          R      4      
Since mobile subscribers cannot detect signals below a minimum threshold level of transmitted power, capping the transmit power of each carrier wave limits how far that carrier wave can travel. Thus, fixing the amount of transmit power limits the cell size that the BTS can serve.
Another drawback of the xe2x80x9cdivide among carriers schemexe2x80x9d is that it uses the overall power allocated to the BTS inefficiently. The power allocated to the unused carriers is wasted when fewer than all of the carriers are in use.
In the event of failure of a power amplifier module in a MCPA, the xe2x80x9cdivide among carriersxe2x80x9d scheme is incapable of compensating for the failure. Typically, the BTS MCPA has several MCPA modules. If one or more of the MCPA modules fails, there is typically not a way for the remaining modules to compensate for the loss of the failed power amplifier modules. Since in that situation there are less power amplifier modules available for the same number of carriers, the actual power supplied to each carrier is less than the power set for the carrier. This reduction in power to each carrier results in an associated reduction in distance that the carrier propagates, and thus the cell site coverage is reduced.
Similarly, the xe2x80x9cdivide among carriersxe2x80x9d scheme does not automatically compensate when additional MCPA modules are installed in the BTS. Since in the xe2x80x9cdivide among carriersxe2x80x9d scheme the amount of power for each carrier has already been set, the installation of additional power supply units does not automatically increase the power per carrier without significant reprogramming of the BTS.
Furthermore, because an MCPA is typically one of the most expensive components of a BTS, it is desirable to deliver a power supply with the minimum number of MCPA modules while retaining the ability to provide maximum transmit power. Minimizing the size of the power amplifier may lower the cost of the power amplifier, which in turn lowers the overall cost of the BTS.
Accordingly, there is a need for a multicarrier power amplifier that can deliver maximum transmit power using the minimum necessary power amplifier. Furthermore, there is need for a multicarrier power amplifier that can automatically compensate for a MCPA module failure and/or the addition of a MCPA module.
An object of the present invention is to provide a method for dynamically allocating radio frequency power to all carriers served by a single BTS.
Another object of the present invention is to provide a method for maximizing coverage area of a BTS by dynamically allocating RF power to each carrier.
It is yet another object of the present invention to prevent saturation and failure of a MCPA, by recognizing the strength of each input signal to the MCPA, and adjusting the gain dynamically to produce maximum output RF power for each carrier.
Another object of the present invention is to provide a system wherein a MCPA can compensate automatically for the failure of individual MCPA modules. It is a further object of the present invention to provide a system whereby a MCPA can compensate automatically for the installation of additional power supply modules.